The invention relates to a torsional actuator and to a method of manufacturing said actuator.
Torsional actuators are known per se. A torsional actuator is a piezo-electric actuator whose end portion is twisted through a small angle under the influence of an electric field. Such a torsional actuator may be in the form of a cuboid with a rigidly secured rectangular rear surface whose dimensions are selected so that the torsional actuator is plate-shaped. If the torsional actuator is put into operation, the side opposite to the rigidly secured side is twisted about its longitudinal axis through the maximum angle of torsion.
In principle, a torsional actuator can be regarded as a combination of two adjacent piezo-electric bending actuators which are interconnected and which comprise electrodes. Torsion occurs when one of the bending actuators is bent in an upward direction while the other bending actuator is bent in a downward direction.
This basic construction is known from U.S. Pat. 4,233,637 in which a simple, cuboidal, single and dual layer bimorphous arrangement is described which can be used as a torsional actuator as well as a bending actuator. This simple bimorphous torsional actuator has the disadvantage that the large layer thicknesses require very high control voltages.
A further actuator is described in the PCT Patent Application WO 89/02658, said actuator being built up of piezo-electric polymer foils whose elastic and piezo-electric properties are such that their use for actuators is subject to certain conditions, because the forces or torques which can be generated are very small. The polymer foils also have a preferred direction in the plane of the layer, which preferred direction is used to attain complicated deformations with simple undivided electrodes. However, only a part of the material or only a few layers of the overall quantity of material can be active, so that the forces which can be generated at a specific volume are relatively small.